Transformer



'Patented Sept. 4, 1.928.

UNITED sTATEs PATENT OFFICE.

FRANK J'. IAEHNI AND 'WILLIAM L. KAEHNI, 0F CLEVELAND, OHIO.

TBANSFOBMEB.

Application led June 8,

The object of' this invention is to provide in a very simple form a variable voltage transformer, whereby with a definite voltage input an desired voltage output, yv1th1n t e limits o the device, may be obtained. Our invention is especially well adapted for u se in heating the filaments of audlons used 1n radio transmission oli-reception, takmg the place of the usual A battery used for this purpose. When so employed the transformer may, for instance, be wound w1th the primary desi ed for 110 volts and connected to a plu soc et or to a flexlble cord having a plug or attachment to an ordinary h ht socket, while the secondary may be woun to give a maximum of 6 volts.

We accomplish the control of the voltage by means of a variable magnetic shunt, which 14s oneof the features of our invention. For radio work it is important to neutralize the cycle hum of the alternating current 1n ut, and to accomplish this we prefer to p ce the entire secondary in series with the lament of 'the audion, but take a tap from the center of the secondary and connect it with the grid', so that., the alternat current through the filament will not i uence the voltage on the grid. The two paths of equal resistance from the grid line to the opposlte so ends of the filament give the same stabilizing eiect as if the circult were connected to the central oint of the filament.

Our mvention is hereinafter more fully described in connection with the accompanying drawings, and its essential characteristics are summarized in the claims.

In the drawings, Fig. 1 is a sectional side elevation of our trans ormer embodied in a sim le form; Fig. 2 is a sectional plan thereof; ig@ is a transformer with the casing in place; Fig. 4 is a plan of the built-up transformer core; Fig. 5 is a cross section through l the rimary of the transformer as indicated bIyl' the line 5-5, Fig. 2. Fig. 6 is a diagram i ustrating the use of the transformer 1n radio wogk. a

The ma etic core of our transformer comprises a c osed circuit member C preferably rectangular.- This member is lamlnated and ma be conveniently made of approximately U-shaped sheet metal stampings, each having an intermediate portion 11 and end legs 12 and 13. The end leg 12 is preferably longer than the leg 13 so that identical stamp- 55 ings may be used to make the complete annulus, the ends of the legs overlapping, as illus- 1922. Serial No. 566,807.

trated in Fig. 4. Suitable non-magnetic bolts 14 may pass throu h the corners of the core to lock the laminatlons together and the two sides of the core member may be held by suitable cross plates 15 and 16 of non-magnetic material secured thereto.

Around one end member of the core bar is the primary winding P which is preferably a single coil mounted between suitable heads 20. The secondary windin s S1 and S2 are placed about the other en member. These windings may be separated by a nonmagnetic plate located between them, and there are preferably end heads 31 at the two outer ends.

Between the primary and secondary windin we extend the core inwardly to make two po e pieces 10, and between these pieces we mount on an intermediate pivot a variably positioned block V of magnetic material. The outer ends of the block and the inner faces of the pole pieces are curved concentrically of the pivot of the block so that the block may stand close to the pole pieces as a magnetic continuation between them, as shown in Fig. 6, or it may be swung to one side, as Ashown in Fig. 2.

WhenV the variator blockis aligning with the pole pieces it forms an effective magnetic shunt for the lines of force from the primary so that com aratively few ofsuch lines pass through t e secondary winding and practically no current is delivered by the secondary. If, however, the variator block be shifted on its pivot, the magnetic path is interrupted and a larger portion of the lines of force pass through the secondary, depending on the extent of `shifting. When the ends of the block are carried well beyond the pole pieces the magnetic path is practically entirely interrupted, and in such case the full voltage strength is obtained from the secondary.

To ivotally mount the variator block as descri. d, we find it convenient'to secure it to a central shaft 40 which may be mounted in the lates 15 and 16 secured to the core. Suitab e means are employed for turning the shaft 40. To enable ittobe adually turned, and also held in any adjuste position against the magnetic pull of the core, we may employ the worm construction shown in Fig. 2. There 43 indicates a suitable worm segment rigid on the shaft 40, while 44 is a worm shaft meshing therewith and mounted in ears 18 and 19 of the plate 15. A suitable collar 45 holds the worm shaft against shifting, `and a knob 46 on thb forward end of the shaft provides means for rotating it.

We have shown the ends of the primary winding as connected to terminals 21 1n a suitable socket 22 adapted to receive pins of a plug 23 on a flexible cord 24. The inner ends of the two secondary colls arc shown as connected together and also connected to a binding post 35, while the outer ends of .the respectlve coils are connected'with binding posts 36 and 37, as shown 1n F 1g. 2, though other terminal arrangements may be made 1f desired.

The structure may be mounted on a suitable base indicated at 50, and maybe readlly secured thereto, for instance, by screws 5l which pass throu rh ears 52 on the heads 20 and 31. The soc et and binding posts may also be carried by thisbase, though other mounting may be used if desired.

It is desirable to encase the transformer mechanism described and to that end we may provide a suitable housing of inverted cupshape indicated at 55, which is shown as extending freely over the coils and core and resting at its lower edge on the base, bemg positioned by a shoulder thereon. The operating shaft 40 may extend through this casing and be provided above the casmgwith a pointer 48 co-operating with graduations on the casing.

Our transformer has a variety of uses but by way of illustration, we have shown in Fig. 6 its employment in heating the filaments of audion bulbs of which two are indicated at A1 and A2. The two filaments are shown as connected in parallel with the complete secondary S1 and S2 by lines a and d which lead from the binding posts 36 and 37. A line e from the binding post 35 at the center of the secondary leads to the grids g and may pass intermediatel through the secondary of the usual amp ifying transformer' T.

With the construction described, if a cord from an ordinary electric light circuit be connected to the socket 22, giving an alternating current of 110 volts to the primary, the secondary may supply, for instance, 6 voltsto the lilament or a less amount, according to the position of the variator V.

a closed magnetic core in substantiallyl rectangular form, a primary winding associated with one leg of the core, a secondary winding associated with the opposite leg, inwardly proJecting pole pieces carried by the remain- 1ng legs of the core, a shaft located midway between the pole pieces, a shunt block of magnetic material carried by the shaft and having curved surfaces complementary to sald pole pieces, the width of the block being substantially equal to the Width of the pole pleces, means associated with the core for supporting said shaft and for holding it in ad]usted position, said means permitting rotation of the shunt block but preventing axial and lateral movement thereof.

2. In a transformer, the combination of a base, a primary winding and a double sec ondary winding supported by the base, a closed circuit magnetic core extendlng through said windings and having inwardly projecting pole pieces between the windings, a bracket member carried by the core, a shaft supported in the base and bracket, a shunt block of magnetic material carried by the shaft between said pole pieces andhaving curved faces complementary to the pole pieces, a transverse shaft carried by thel bracket, a worm screw and segment between the two shafts for positioning and holding the block in varying angular relationship to the pole pieces, and terminals mounted on the base outside of the casing, there being two. such terminals for the primary and three for the secondary windings.

In testimony whereof, we hereunto ailix our signatures.

FRANK J. KAEHNI. WILLIAM L. KAEHNI. 

